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Kornyeyev D, El-Bizri N, Hirakawa R, Nguyen S, Viatchenko-Karpinski S, Yao L, Rajamani S, Belardinelli L. Contribution of the late sodium current to intracellular sodium and calcium overload in rabbit ventricular myocytes treated by anemone toxin. Am J Physiol Heart Circ Physiol 2016; 310:H426-35. [DOI: 10.1152/ajpheart.00520.2015] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/07/2015] [Accepted: 12/02/2015] [Indexed: 12/19/2022]
Abstract
Pathological enhancement of late Na+ current ( INa) can potentially modify intracellular ion homeostasis and contribute to cardiac dysfunction. We tested the hypothesis that modulation of late INa can be a source of intracellular Na+ ([Na+]i) overload. Late INa was enhanced by exposing rabbit ventricular myocytes to Anemonia sulcata toxin II (ATX-II) and measured using whole cell patch-clamp technique. [Na+]i was determined with fluorescent dye Asante NaTRIUM Green-2 AM. Pacing-induced changes in the dye fluorescence measured at 37°C were more pronounced in ATX-II-treated cells than in control (dye washout prevented calibration). At 22–24°C, resting [Na+]i was 6.6 ± 0.8 mM. Treatment with 5 nM ATX-II increased late INa 8.7-fold. [Na+]i measured after 2 min of electrical stimulation (1 Hz) was 10.8 ± 1.5 mM and 22.1 ± 1.6 mM ( P < 0.001) in the absence and presence of 5 nM ATX-II, respectively. Inhibition of late INa with GS-967 (1 μM) prevented Na+i accumulation. A strong positive correlation was observed between the late INa and the pacing-induced increase of [Na+]i ( R2 = 0.88) and between the rise in [Na+]i and the increases in cytosolic Ca2+ ( R2 = 0.96). ATX-II, tetrodotoxin, or GS-967 did not affect [Na+]i in quiescent myocytes suggesting that late INa was solely responsible for triggering the ATX-II effect on [Na+]i. Experiments with pinacidil and E4031 indicate that prolongation of the action potential contributes to as much as 50% of the [Na+]i overload associated with the increase in late INa caused by ATX-II. Enhancement of late INa can cause intracellular Na+ overload in ventricular myocytes.
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Affiliation(s)
- Dmytro Kornyeyev
- Department of Biology, Gilead Sciences Inc., Foster City, California
| | - Nesrine El-Bizri
- Department of Biology, Gilead Sciences Inc., Foster City, California
| | - Ryoko Hirakawa
- Department of Biology, Gilead Sciences Inc., Foster City, California
| | - Steven Nguyen
- Department of Biology, Gilead Sciences Inc., Foster City, California
| | | | - Lina Yao
- Department of Biology, Gilead Sciences Inc., Foster City, California
| | | | - Luiz Belardinelli
- Department of Biology, Gilead Sciences Inc., Foster City, California
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Han C, Estacion M, Huang J, Vasylyev D, Zhao P, Dib-Hajj SD, Waxman SG. Human Na(v)1.8: enhanced persistent and ramp currents contribute to distinct firing properties of human DRG neurons. J Neurophysiol 2015; 113:3172-85. [PMID: 25787950 DOI: 10.1152/jn.00113.2015] [Citation(s) in RCA: 77] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2015] [Accepted: 03/13/2015] [Indexed: 12/19/2022] Open
Abstract
Although species-specific differences in ion channel properties are well-documented, little has been known about the properties of the human Nav1.8 channel, an important contributor to pain signaling. Here we show, using techniques that include voltage clamp, current clamp, and dynamic clamp in dorsal root ganglion (DRG) neurons, that human Na(v)1.8 channels display slower inactivation kinetics and produce larger persistent current and ramp current than previously reported in other species. DRG neurons expressing human Na(v)1.8 channels unexpectedly produce significantly longer-lasting action potentials, including action potentials with half-widths in some cells >10 ms, and increased firing frequency compared with the narrower and usually single action potentials generated by DRG neurons expressing rat Na(v)1.8 channels. We also show that native human DRG neurons recapitulate these properties of Na(v)1.8 current and the long-lasting action potentials. Together, our results demonstrate strikingly distinct properties of human Na(v)1.8, which contribute to the firing properties of human DRG neurons.
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Affiliation(s)
- Chongyang Han
- Department of Neurology, Yale University School of Medicine, New Haven, Connecticut; and Center for Neuroscience and Regeneration Research, Veterans Affairs Medical Center, West Haven, Connecticut
| | - Mark Estacion
- Department of Neurology, Yale University School of Medicine, New Haven, Connecticut; and Center for Neuroscience and Regeneration Research, Veterans Affairs Medical Center, West Haven, Connecticut
| | - Jianying Huang
- Department of Neurology, Yale University School of Medicine, New Haven, Connecticut; and Center for Neuroscience and Regeneration Research, Veterans Affairs Medical Center, West Haven, Connecticut
| | - Dymtro Vasylyev
- Department of Neurology, Yale University School of Medicine, New Haven, Connecticut; and Center for Neuroscience and Regeneration Research, Veterans Affairs Medical Center, West Haven, Connecticut
| | - Peng Zhao
- Department of Neurology, Yale University School of Medicine, New Haven, Connecticut; and Center for Neuroscience and Regeneration Research, Veterans Affairs Medical Center, West Haven, Connecticut
| | - Sulayman D Dib-Hajj
- Department of Neurology, Yale University School of Medicine, New Haven, Connecticut; and Center for Neuroscience and Regeneration Research, Veterans Affairs Medical Center, West Haven, Connecticut
| | - Stephen G Waxman
- Department of Neurology, Yale University School of Medicine, New Haven, Connecticut; and Center for Neuroscience and Regeneration Research, Veterans Affairs Medical Center, West Haven, Connecticut
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Moreau A, Krahn AD, Gosselin-Badaroudine P, Klein GJ, Christé G, Vincent Y, Boutjdir M, Chahine M. Sodium overload due to a persistent current that attenuates the arrhythmogenic potential of a novel LQT3 mutation. Front Pharmacol 2013; 4:126. [PMID: 24098284 PMCID: PMC3787509 DOI: 10.3389/fphar.2013.00126] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2013] [Accepted: 09/11/2013] [Indexed: 12/21/2022] Open
Abstract
Long QT syndrome (LQTS) is a congenital abnormality of cardiac repolarization that manifests as a prolonged QT interval on 12-lead electrocardiograms (ECGs). The syndrome may lead to syncope and sudden death from ventricular tachyarrhythmias known as torsades de pointes. An increased persistent Na+ current is known to cause a Ca2+ overload in case of ischemia for example. Such increased Na+ persistent current is also usually associated to the LQT3 syndrome. The purpose of this study was to investigate the pathological consequences of a novel mutation in a family affected by LQTS. The impact of biophysical defects on cellular homeostasis are also investigated. Genomic DNA was extracted from blood samples, and a combination of PCR and DNA sequencing of several LQTS-linked genes was used to identify mutations. The mutation was reproduced in vitro and was characterized using the patch clamp technique and in silico quantitative analysis. A novel mutation (Q1476R) was identified on the SCN5A gene encoding the cardiac Na+ channel. Cells expressing the Q1476R mutation exhibited biophysical alterations, including a shift of SS inactivation and a significant increase in the persistent Na+ current. The in silico analysis confirmed the arrhythmogenic character of the Q1476R mutation. It further revealed that the increase in persistent Na+ current causes a frequency-dependent Na+ overload in cardiomyocytes co-expressing WT and mutant Nav1.5 channels that, in turn, exerts a moderating effect on the lengthening of the action potential (AP) duration caused by the mutation. The Q1476R mutation in SCN5A results in a three-fold increase in the window current and a persistent inward Na+ current. These biophysical defects may expose the carrier of the mutation to arrhythmias that occur preferentially in the patient at rest or during tachycardia. However, the Na+ overload counterbalances the gain-of-function of the mutation and is beneficial in that it prevents severe arrhythmias at intermediate heart rates.
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Affiliation(s)
- Adrien Moreau
- Centre de Recherche de l'Institut Universitaire en Santé Mentale de Québec, Quebec City QC, Canada
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Shryock JC, Song Y, Rajamani S, Antzelevitch C, Belardinelli L. The arrhythmogenic consequences of increasing late INa in the cardiomyocyte. Cardiovasc Res 2013; 99:600-11. [PMID: 23752976 DOI: 10.1093/cvr/cvt145] [Citation(s) in RCA: 97] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
This review presents the roles of cardiac sodium channel NaV1.5 late current (late INa) in generation of arrhythmic activity. The assumption of the authors is that proper Na(+) channel function is necessary to the maintenance of the transmembrane electrochemical gradient of Na(+) and regulation of cardiac electrical activity. Myocyte Na(+) channels' openings during the brief action potential upstroke contribute to peak INa and initiate excitation-contraction coupling. Openings of Na(+) channels outside the upstroke contribute to late INa, a depolarizing current that persists throughout the action potential plateau. The small, physiological late INa does not appear to be critical for normal electrical or contractile function in the heart. Late INa does, however, reduce the net repolarizing current, prolongs action potential duration, and increases cellular Na(+) loading. An increase of late INa, due to acquired conditions (e.g. heart failure) or inherited Na(+) channelopathies, facilitates the formation of early and delayed afterpolarizations and triggered arrhythmias, spontaneous diastolic depolarization, and cellular Ca(2+) loading. These in turn increase the spatial and temporal dispersion of repolarization time and may lead to reentrant arrhythmias.
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Affiliation(s)
- John C Shryock
- Department of Biology, Cardiovascular Therapeutic Area, Gilead Sciences, Foster City, CA, USA
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Lariccia V, Moraca A, Marini M, Nasti AA, Battistoni I, Amoroso S, Perna GP. Unusual case of severe arrhythmia developed after acute intoxication with tosylchloramide. BMC Pharmacol Toxicol 2013; 14:8. [PMID: 23347670 PMCID: PMC3566980 DOI: 10.1186/2050-6511-14-8] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2012] [Accepted: 01/21/2013] [Indexed: 01/09/2023] Open
Abstract
Background Drugs not commonly considered to be cardioactive agents may cause prolongation of the QT interval with resultant torsades de pointes and ventricular fibrillation. This form of drug toxicity often causes cardiac arrest or sudden death. Case presentation After accidental ingestion of tosylchloramide a caucasian 77-year-old woman, with a family history of cardiovascular disease and hypertension, was admitted to the intensive care unit following episodes of torsades de pointes with a prolonged QT/QTc interval (640/542 ms). The patient received an implantable cardioverter-defibrillator, was discharged from the hospital with normal QT/QTc interval and did not experience additional ventricular arrhythmias during one year of follow-up. Conclusion This is the first report concerning an unusual case of torsades de pointes after accidental intoxication by ingestion of tosylchloramide. The pronounced impact of the oxidyzing agent tosylchloramide on the activity of some of the ion channels regulating the QT interval was identified as a probable cause of the arrhythmia.
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Affiliation(s)
- Vincenzo Lariccia
- Department of Biomedical Sciences and Public Health, University Politecnica delle Marche, Ancona, Italy
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